Magnetostrictive electroacoustic transducer



Oct. 19, 1948. I A. MURDOCH, JR I 2,451,958 MAGNETOSTRICTIVE ELECTROACOUSTIC TRANSDUCER Filed Jan. 3, 1940 Patented Oct. 19, 1948 insists MAGNETOSTRICTEVE ELEfiTROACQUSTEC TRANSDUCER Alexander Murdoch, Jn, Philadelphia, Pa... assignor to Radio Corporation of America, a corporation of Delaware Application January 3, 1940, Serial No. 312,297

9 (llalms.

This invention relates to magnetostrictive electroacoustic transducers and more especially to a magnetostrictively driven transducer for underwater signalling.

It is well known that electroacoustic transdrive th diaphragm, various phasing problems arise.

. it is one of the objects of this invention to provide an improved magnetostrictive electroacoustic transducer. Another object is to provide means for driving a. large diaphragm at high efiiciency by a plurality or properly spaced and phased magnetcstrictive elements. Another object is to provide an efficient electroacoustic transducer for generating a sharply defined compressional wave in water. An additional object is to provide the optimum geometrical arrangementoi a plurality of magnetostrictlve elements for driving 9. diaphragm or to be driven thereby.

The invention will be described by referring to the accompanying drawing in which Fig. 1 is a sectional view of one embodiment of the invention; Figure 2 is a plan view of the diaphragm and magnetostrictive element arrangement; Figure 3 is a graphic illustration used in describing the invention; and Figure 4. is a wiring diagram of one arrangement of operating coils and polarizlng means therefor.

Referring to Fig. l, the electrcacoustic transducer is included within a spherical housing of three parts: the front part i. central part 3 and rear part 5. The three parts are separated by rubber gaskets l. The front part land the central part 8 are clamped together by circumferentially distributed cap screws ii. The gasket 7 between the front and central parts of the housing includes an annular recess ii within which is clamped a heavy diaphragm it. The diaphragm it has one or more recessed portions i adjacent the circumference. The recessed portions and the rubber gasket provide flexibility for the diaphragm mounting. The space between the diaphragm is and the front part i is filled with a liquid to increase the forward radiation of the device.

of the arcuate member thereto.

The rear part of the housing is secured to the central part b means oi an arcuate member 97 which is fastened to the rear part by a cap screw it and to the central part by welding the ends 2i The arcuate member i1 may be reinforced by a rib 28. The central part includes a back plate 25. The portion of the back plate next to the rear part of the housing. includes a small air chamber 2? and a light weight diaphragm 29. he s ace between the diaphragm 2t and the rear part B 01' the housing forms an air chamber to reduce radiation toward the rear. The central part of the housing also includes a shoulder iii upon whichis mounted an insulated supporting member 33. A plurality of coils 35 are suitably mounted on the supporting member. Each of the coils is coaxially arranged with respect to the magnetostrictive elements 3'? as'hereinafter described.

A plurality of magnetostrictive elements 3? are fastened to the rear portion of the diaphragm is by welding, soldering, brazing, or the like 38. The elements are preferably nickel-steel tubes of an efiective length equal to a quarter of the length of the wave to be radiated. The lower portion of each of the elements is slotted adjacent the actuating and magnetizing coils to reduce losses therein. The free ends of the elements 3? are spaced from the back plate 25 to permit free movement upon application oi the driving forces. The tubular elements transfer the magnetostrictive forces to the diaphragm which, due to its large mass and to th impedance of the sound medium, moves through very short distances.

In order that the diaphragm move as a whole, it is desirable that the driving forces be suitably applied to the diaphragm at many points. It is also desirable to apply'the forces efiiciently. If the elements are arranged in groups forming equilateral triangles, with common sides, it has been found that the forces are applied with maximum efliciency. The plurality of triangles are arranged as shown in Fig. 2. A single triangular arrangement of elements A. B and C is shown in Fig. 3. If the broken line circles AA, BB and CC, which are tangent to each other, represent the spheres of influence or forces applied by or to the respective elements, it follows that less diaphragm area X is uninfluenced than by any other geometric arrangement of a plurality of diaphragm driving units. Furthermoraif other triangles are arranged common to each side of A, B, C, it follows that the added triangles are again the optimum geometric arrangement for applying the magnetostrictive forces to the diaphragm.

are large compared to the diaphragm movements.

It, therefore, follows that the elements act as transformers of the applied force. If the power is to be applied without excessive losses, the walls of the tubular elements must be sufficiently thick to transfer the applied power. and sufficiently light to properly match the several impedances of the transformer and diaphragm. By way of example, 320 nickel-steel tubes, having a wall thickness of 0.20 inch, an external diameter of of an inch, and a length of 2 inches. have been used in a transducer operating in sea water at a wave length of approximately 6 inches.

The coils are energized by direct current, as from batteries I8, '39 and 10; to apply a magnetizing force to the magnetostrictive elements. The coils may be energized by alternating currents from a suitable source ll representing the signals to be radiated, or, if received signals are impressed on the diaphragm, currents corresponding to the signals may be derived from the magneto forces applied to the coils. The several coils may be connected in series-parallel arrays, as shown in Figure 4, for example, and energized in such proportions through the use of the polarizing batteries 38, ll, 40 and signal attenuatin resistors 42 and of diflerent magnitudea'for example, as will best drive the diaphragm as a .wl

Thus the invention has been described as an electroacoustic transducer in which the diaphragm is driven by a plurality of magnetostrictive elements. The elements are disposed geometrically-to apply driving forces most efficiently. The device may be operated by reception, in which case the forces driving the diaphragm establish signal currents in the coils used to energize the elements.

I claim as my invention: 1. An electroacoustic transducer including a tween said central part and said rear part, the

free end of said elements lying adjacent the inner surface of said back plate; means establishing a plurality of separate air chambers located successively between said back plate and the rear part of said housing; an energizing coil in energy transfer relation with each of said elements; and a non-compressible liquid substantially filling said front part, whereby vibratory energy may be transmitted between the medium surrounding said housing and said heavy diaphragm through said non-compressible liquid, and the transmission of said energy through said 'rear part is effectively prevented.

5. A device of the character described in claim 4 in which said means establishing a plurality of separate air chambers comprises a lightweight diaphragm mounted in spaced parallel relation to the outer surface of said back plate and lying within said rear part, and an arcuate member mounted within said rear part in uniformly spaced relation to the inner surfac thereof.

6. In an electroacoustical transducer, a housing part comprising a hollow member, a vibratory diaphragm wholly within and closing on a portion of the interior at one end of said member, a plate within said member and closing of! a" portion of the other end of said member, electro-mechanical conversion means within said member interposed 1 between said diaphragm and said plate and coupled to said diaphragm either for actuating said diaphragm, a plurality of magnetostrictive elements attached to said diaphragm so that the points of attachment form a plurality of equilateral triangles having a number of common sides, said elements being so distributed over said diaphragm that the spheres of influence of adiacent elements border each other, and means for energizing said elements.

2. An electroacoustic transducer including a diaphragm, a plurality of tubular magnetostrictive elements attached to said diaphragm so that their axes are normal to the surface of the dia- Dhragm and so that the points of attachment form a plurality of equilateral triangles having a number of common sides, said elements being so distributed over said diaphragm that the spheres of influence of adjacent elements border each other, and coil means surrounding each of "said elements forapplying'thereto magnetizing forces.

3. An electroacoustic transducer including a diaphragm, a plurality of magnetostrictive elements attached to said diaphragm so that the points of attachment form a plurality of equilateral triangles having a number of common sides, said elements being made of tubular material having a slot therein and being so distributed oversaid diaphragm that thes'phe'res of influence of adjacent elements border each ot her, and a plurality of coils a separate one of which surrounds ea'ch of said elements, said coils being ardiaphragm in response to electrical signal energy supplied thereto or adapted to be energized by said diaphragm upon vibration thereof, and a second diaphragm connected to said plate in spaced relation thereto and lying within the closed off portion at said other end of ,said member whereby to provide an air chamber therebetween. 4

7. In an electroacoustical transducer, a housing part comprising a hollow member, a vibratory diaphragm wholly within and closing off a portion of the interior'of one end of said member, a plate within said member and closing off a portion of the other endof said member. electro-meehanical conversion means within said member interposed between said diaphragm and said plate, said conversion means including a pluralit of magnetostrictive elements secured to said diaphragm either for actuating said diaphragmin response to electrical signal energy supplied thereto or v adapted to'b'e energized by said diaphragm upon ranged to permit free movement of the elementsunder the influence of magnetostl'lctive' forces,

vibration thereof, and a second diaphragm connected to said, plate .in spaced relation thereto and lying within the closed off portion at said other end of said member, whereby to provide an air chamber therebetween.

' 8. In an electroacoustlcal transducer of the magnetostrictive type, the. combination of a vibratory diaphragm, a plurality of magnetostrictive elements distributed over the area of and attached to said diaphragm, and a plurality of coils a separate one 'of 'which surrounds each of sa d elements, each one of said coils being 'adaptassume 5 ed to influence its associated element to actuate said diaphragm over substantially a predetermined circular area, and the points oi attachment or said elements to'said diaphragm being so spacedthat the perimeters or said circular areas are tangenttoeach other.

9. In an electroacoustical transducer of the magnetostrictive type. the combination of a vibratory diaphragm, a plurality of magnetostrictive elements distributed over the area 01' and attached to said diaphragm, and a plurality oi! coils a separate one of which surrounds each of said elements, each one of said coils being adapted to influence its associated element to actuate said diaphragm over substantially a predetermined circular area, and the points of attachment of said elements to said diaphragm being so spaced that the perimeters of said circular areas iacent ones of said points form equilateral triangles of which adiacent triangles have common sides. I

ALEXANDER MURDOCH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 768,568 Mundy Aug. 23, 1904 1,591,068 Williams July 6, 1926 2,014,413 Pierce Sept. 17, 1935 2,063,949 Pierce Dec. 15, 1926 15 2,374,637 Hayes Apr. 24, 1945 2,405,472 Tuttle a. Aug. 6, 1946 2,407,256 Dallin Sept. 10, 1946 FOREIGN PATENTS Number Country Date 818,799 "France Nov. 29, 1926 Certificate of Correction Patent No. 2 451368 October'lQ, 19 423 ALEXANDER MURDOCH, JR.

It is hereby certified that error appears in the printed specification of theabove numbered patent requiring correction as follows:

Column 3, line 12, for 0.20 inch read .020 inch; line 37, for the Word by before reception read for; column 6, list of foreign references cited, add the following- 145,691 Great Britain -July 28, 1921 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 24th day of October, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Oommz'ssioner of Patents.

Certificate of Correction Patent No. 2,451,968 October 19, 1941??" ALEXANDER MURDOCH, JR. It is hereby certified that error appears in the printed specification of theabove numbered patent requiring correction as follows:

Column 3, line 12, for 0.20 inch read .020 inch; line 37, for the Word by before reception read for; column 6, list of foreign references cited, add the following 145,691 Great Britain July 28, 1921 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 24th day of October, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Commz'sstoner of Patents. 

